The process of extrusion comprising charging solid extrudable material, such as rubber, to a heat chamber of an extruder is well known in the art. The material is heated in the chamber to a flowable state and forced from the chamber through an opening in a die assembly by a rotatable screw. The extrudate is then removed using a conveyor system.
In the past, extruded products having a profile, such as rubber automobile and refrigerator door seals, have been limited to linear extruded configurations. To obtain profile seals having angular configurations, for example, individual lengths of linear extrudate were joined at their respective ends to create corners or bends to form the final seal shape, such as by a separate molding step. The additional process step increased the time and expense of manufacture and created potential operational problems. Specifically, the corner junctions of the final product might be weaker than the component lengths, which could result in potential seal failure points, or the junctions might have deformed or distorted cross-sectional configurations relative to the cross section of the extrudate lengths which are unattractive in appearance, and could cause a reduction in seal efficiency.
The discovery of a method and apparatus for continuously manufacturing curved or bent extrusions having undistorted cross-sectional shapes, as set forth in co-pending patent application Ser. No. 07/207,838 to Miller (assigned to the assignee of the present application), eliminated the problem of joining extrudate lengths to make curvatures or bends. However, several problems still exist with respect to changing the profile of the extrudate being manufactured.
The process of changing the profile of an extruder die assembly, or the extrudate material exiting the die assembly, typically requires shutting down the extruder and extrusion process line. If the die change takes an appreciable amount of time, it may be necessary to purge hot material from the extruder to prevent unwanted crosslinking or degradation reactions in the extrudate material. It may also be necessary for the extrudate already manufactured, but not yet completed, to be transported through the remainder of the manufacturing line by a conveyor, or other conventional method, to complete the curing, cooling or crosslinking process. Under these circumstances, restarting the line may require extrudate already manufactured to be feed by hand through the line to form a continuous extrudate. This process is time consuming and may result in considerable extrudate material being wasted. The extruder may also require cleaning to begin extrusion of a different extrudate material. This process may take from 15 minutes to several hours, depending on whether or not the extruder must be purged or the line broken, in addition to any desired profile changes.